Spring Introduction

Tác giả
• Rob Johnson
• Based on his book : Expert One-on-One J2EE
Design

What’s Spring
• Java Application Framework
• Spring core build on Dependency Injection
Pattern
• Many modules

Dependency Injection
• A class should not configure its dependencies
statically but should be configured from
outside
• If a class directly creates an instace of anohter
class via the new operator, it cannot be used
(and tested) independently

Problem
class DAOUser{
private DataSource dataSource
private DAOUser(){
dataSource = new MySQLDataSource();
datsSource.set(..some..properties);
}
}
DAOUser MySQLDataSource

Constructor Injection
class DAOUser{
private DAOUser(DataSource dataSource){
this.dataSource = dataSource
}
}
Easier to test
DAOUser DataSource

Injection
class DAOUser{
private DAOUser(DataSource dataSource){
}
}
OR
class DAOUser{
private void setDataSource(DataSource dataSource){
}
}
DAOUser DataSource

Injector 
class DAOInjector{
public void inject(){
DataSource dataSource = new DataSource();
DAOUser daoUser = new DAOUser(dataSource);
}
}
DAOUser DataSource
DAOInjector

Injector in Spring
class DAOUser{
@Autowired
private DataSource dataSource;
//setter for dataSource
...
}
@Component
class MySQLDataSource extends DataSource{
}

Spring Introduction

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